The present invention relates to an apparatus for closing and/or regulating the tapping of molten metal from the interior of a metallurgical vessel. More particularly, the apparatus includes a vertical inner refractory fireproof pipe which has therethrough, at a level above the bottom of the metallurgical vessel, at least one lateral opening for the passage of molten metal. An outer refractory fireproof pipe is fitted over the inner pipe and has extending through the wall thereof at least one lateral opening for the passage of the molten metal. One of the pipes is to be mounted stationarily in the bottom of the metallurgical vessel to extend vertically upwardly into the interior of the vessel. The other of the pipes is displaceable relative to the stationary pipe in a vertical axial direction through a working stroke within which the openings in the two pipes may be brought into alignment to thereby discharge molten metal downwardly through the interior of the inner pipe.
An apparatus of this general type is disclosed in German DE 35 40 202 Cl wherein an opening of a stationary inner pipe is just as large as an opening in a displaceable outer pipe. During the working stroke the molten metal passes from the vessel bottom into the inner pipe. To control the discharge or tapping of the molten metal, the opening or openings in the outer pipe are brought more or less into alignment with the opening or openings in the inner pipe. Several openings can be provided in order to clean the openings by means of an intensive flow of molten metal.
German DE 37 31 600 Al discloses a rotary nozzle including a stationary outer pipe and an inner pipe that is displaceable in a longitudinal direction. For rapid passage of the molten metal, the stationary outer pipe has an opening the cross section of which is greater than that of its other opening and of the opening in the displaceable inner pipe. To make the opening with the larger cross section effective, the inner pipe is displaced to a position such that its opening no longer has an effect on the molten metal discharge.
In known apparatus of this type, the speed at which the melt is discharged is strongly dependent on the height or level of the bath of molten metal within the vessel, i.e. hydrostatic pressure of the molten metal. Since the discharge height above the bottom of the vessel, and thereby from the upper level of the molten metal, is determined by the height of the opening through the stationary pipe, the speed of discharge of molten metal is higher for a higher bath level than for a lower bath level. This reduction in discharge speed as the bath level lowers results in a reduction in quality of the discharged metal, and particularly a reduction in steel grade when the molten metal is steel.